Solenoids used in electronic locks typically act to displace some member of the mechanical controls of the lock such that the remainder of the mechanical controls in the lock may function to withdraw the bolt and thereby open the lock. Some solenoids that have been used in previous electronic locks required either prolonged current flow through the solenoid to maintain the solenoid in its activated or actuated position, or a mechanical latching mechanism to hold the activated mechanism in its activated position until the lock is physically opened. A latch typically requires a reset input to return the lock to its locked secured condition.
Solenoids of the push type typically have an armature which, upon the actuation of the solenoid by an electrical voltage applied thereto, extends from the body of the solenoid. The solenoids attract or pull an armature toward the solenoid housing and body; and, if the armature is such that it is pulled into contact with the body of the solenoid and no restore force is applied to the solenoid armature, then the armature seals and remains sealed to the solenoid body even after the electrical potential and current are removed from the solenoid. This sealing of the armature plate to the solenoid body commonly found on most push-type solenoids is referred to as a magnetic seal.
Solenoids of the push-type typically are supplied from the manufacturer with a relatively thin, non-magnetic spacer or shim interposed between the armature plate and the solenoid body to prevent the armature plate from making contact with the solenoid body. This spacer keeps the armature plate sufficiently away from the body so that whenever the activating voltage is removed, any residual magnetic field in the housing and core of the solenoid will be displaced from the solenoid armature plate sufficiently that the residual magnetic field cannot hold the solenoid armature in a sealed position. On the other hand, without the spacer present, the armature plate seals against the solenoid body, and there may be insufficient mechanical restoration force available to reset the solenoid to its unactuated position. Accordingly, the armature will remain in its actuated or picked position and will maintain the set condition whereby the lock is conditioned for opening and, therefore, is unlocked and insecure.
In locks using the sealing characteristic of the solenoid without the spacer, mechanical resets are necessary to break or overcome both the residual magnetic attraction force and the sealing of the armature and armature plate to the solenoid body. In order to accomplish the resetting function, mechanical resets require some action such as a manual operator input or the withdrawal of the bolt. If the armature plate is sealed to the solenoid body and there is either insufficient or no mechanical force applied to the armature to cause it to reset to its unactuated position, then the residual magnetism found in a solenoid which does not have a non-magnetic spacer may hold the armature in the actuated position.
If the solenoid is first activated and then restores under a sufficiently strong mechanical reset force immediately upon the deactivation of the solenoid's voltage source, the lock components and particularly the solenoid armature will reset and any displaced mechanical elements which are not latched in place, similarly will reset. This results in a lock which is only subject to being opened while the voltage potential is applied to the solenoid and the armature is in its actuated position.
The maintaining of a continuous voltage potential and current flow on and through the solenoid is a substantial power constraint on the design of the self-powered locks wherein all the power necessary to operate all aspects of the lock is derived from a manually operated electrical generator. Locks which are self-powered and have a manually operated generator contained within the lock typically are incapable of maintaining any substantial voltage and current flow for any significant length of time and, therefore, it is impractical to maintain an actuating current for a time sufficient for the operator to withdraw the bolt and, for battery powered locks, the battery life is substantially reduced.